Objective To explore the lethal activity of propylene glycol alginate(PGA)and its mixed liquor with beta-cypermethrin against Haemaphysalis longicornis larvae, the aim was to evaluate the potential activity of PGA on killing ticks. Methods Mixed liquor was made with the ratio between beta-cypermethrin and PGA 1:1, 1:2, 2:1. Experimental group includes these three mixed liquor, PGA and beta-cypermethrin while the control is pure water. Spray tick larvae on culture dishes with these liquor, and then observed the mortality of ticks in different time series. Results There was no significance at any time series between high dilution of beta-cypermethrin(1 000 mg/L) and low dilution of PGA(12 mg/L) (Mann-Whitney U=7, P=0.766), and between high dilution of beta-cypermethrin(250 mg/L) and low dilution of PGA (2.4 mg/L) (Mann-Whitney U=4, P=0.240). However, the early efficiency(0.5 h) of PGA was significantly lower than beta-cypermethrin(χ²=7.670, P=0.007). The efficiency at 24 h and 48 h were the same between PGA and beta-cypermethrin(χ²=3.453, P=0.063; χ²=3.560, P=0.059). The efficient of mixed liquor C(ratio between PGA and beta-cypermethrin was 1:2) was the best of all. Conclusion PGA could kill the long-horned qinghaiensis ticks larvae, but it was not quick effect. According to the result, the most efficient ratio between beta-cypermethrin and PGA was 2:1.